- Allow at least 3 packets and up to half the window to be active resends
     instead of just 1, to reduce stall time after a packet drop
   - Increase fast retransmit threshold back to 3 to reduce retransmissions
   - Don't fast retransmit if we recently retransmitted it already
   - Allow double the window as long as gaps are less than the window
   - Don't set the MSS in a resent packet (saves 2 bytes)
   - Remove redundant calls to updateAcks()
   - Update activity timer when resending a packet
   - Reset unackedPacketsReceived counter at all places where acks are sent
     so it isn't wrong
   - Fix some places where the activeResends count could become wrong
   - Prevent storm of CLOSE packets
   - Never resend the whole packet in ackImmediately(), just send an ack
   - Cancel flusher timer in MessageOutputStream when closed
   - Move some createRateStats to ConnectionManager to reduce repeated calls
   - Cleanups, javadocs, logging, volatile, finals